This paper provides an analysis of global warming policy as the provision of a global public good. Using a regional model composed of thirteen world regions, the paper shows how disparate incentives among the regions hinder a shift from a Business As Usual (BAU) policy to a Globally Optimal Policy (GOP). In the BAU scenario, there will be large variations in impacts from warming across the regions, meaning some countries have little incentive to participate in collective agreements. Under the GOP scenario, negative impacts from global warming will be significantly reduced in some regions resulting in strong incentives for these regions to press for action. The paper finds that an optimal regulation could save Europe, India, and Africa hundreds of billions of dollars per year by the end of this century, but would cause additional costs to China, Russia, Canada and the USA. Under the optimal regulatory framework, higher levels of abatement are required for developing countries, worsening the existing climate equity problem.